1. Technical Field of the Invention
The present invention relates to a color image reading apparatus, and more particularly, to a color image reading apparatus which is adapted to reading a color image of a film and is provided with imaging means for reading a color image formed by an optical system as color separation signal of three colors on each picture element.
2. Description of Related Art
When a color image formed by an optical system is read, there appears characteristic phenomena in color film different from an ordinary reflection type original. For example, even if a color film is used for the same subject to be photographed, transmission density of the film differs depending on an exposure condition under which it is photographed. A balance among lights of red, green and blue (hereinafter called as R, G, B) in a photographed color image differs depending on a kind of film whether it is negative or positive, and depending on a difference in sensitivity.
In Japanese Published Unexamined Patent Application No. 65374/1990, there is disclosed an apparatus which is arranged to correct a data of an image which has been read by the difference between a standard value preliminarily set and a digital image signal which is based on an image read wherein a standard lookup table (hereinafter called as LUT) is provided to correct the difference when a color image is read. However, such a conventional apparatus requires expensive cost for providing circuits since memories for said standard LUT have to be prepared for the number of kinds of films.
When an image reading data is corrected by said LUT corresponding to a kind of film, a kind of film has to be inputted for an image to be read one by one which requires complicated operations, and an apparatus becomes complicated to eventually cause to raise manufacturing cost of the apparatus.
Moreover, if a correction is uniformly conducted by a standard value preliminarily set, even if a scenery photographed has weak contrast, for instance, the contrast becomes stronger since such a uniform correction is performed, and an output a photographer intended can not be displayed. In a film image, when a balance among R, G, and B is broken down like a .scenery of sunset glow, even if a balance of image data among R, G, and B which have been read is uniformly corrected, an output a photographer aimed can not be displayed.
In most cases, special films such as positive film, 4.times.5-inch film or 6 cm film are used by a specialist. In a photograph taken by a specialist, a balance is intentionally broken and a peculiar exposure condition is set. Therefore, if a correction is uniformly conducted in such a case, an output different from the one the specialist intended is not displayed.